The concept of paint roller applicators is well known in the art. In general, a paint roller applicator includes a frame with a handle for a user to grasp the applicator and an absorbent cover or roller rotatably mounted on the end of the frame to permit a user to roll paint onto a surface. The need for frequently removal of rollers for cleaning necessitates their mounting on a wire cage-bearing mechanism through a friction fit between the wire cage bearing and the interior core of the paint roller. The friction fit allows a user to slip the roller on or off manually. This procedure works well for large-diameter paint rollers, such as the conventional one-and-one-half inch diameter paint rollers.
One of the difficulties with manufacturing small-diameter paint rollers for use in tight places is that the bearing must also have a small diameter. Unfortunately, decreasing typical wire cage-bearing mechanisms, which are usually about one- and one-half inches in diameter, to a smaller diameter is both difficult and costly.
Also, a smaller sized bearing mechanism may not properly hold the paint roller in a rotatable position on the frame of the paint roller applicator unless the tolerances necessary to produce a slide fit between the roller and the bearing also decrease. Generally, the tolerances for frictional fit between the core and the bearing become increasingly critical as the diameter of the paint roller core decreases. Without careful control, the fit of the paint roller on the bearing may be incorrect--either too tight or too loose. Closely controlling tolerances of wire bearings increases their manufacturing costs.
In general, paint roller applicators are relatively inexpensive. For consumer acceptance, component costs must be low. One method of reducing costs is injection molding of bearings out of plastics. The small degree of working pressure applied to bearings permits their manufacture from inexpensive grades of plastic. However, molding the bearings from inexpensive, weaker plastics has two drawbacks. First, the need to assemble the bearing on an axle usually requires force, necessitating the use of more expensive, stronger plastics.
Second, plastic injection molds are very costly and complex. To achieve internal holes or undercuts in more than one plane requires incorporation of slides, cores or other means into an injection mold. This greatly increases the cost and the required maintenance on the mold. The best design for a plastic part requires a mold without complex slides or cores. Unfortunately, the bearings require a central opening and other irregular features, making molding of plastic bearings expensive. Consequently, manufacturing plastic paint roller bearings with an axial opening requires additional labor costs, since this method of manufacturing requires a retractable core to form the axial opening in the bearing. Extra labor costs not only increase bearing costs but may prevent the manufacturer from molding the bearing in the United States. If the added labor costs make the price too high, the manufacture may resort to cheaper fabrication offshore to overcome the inefficiencies of molding.
Thus, the combination of the need for a high grade plastic for strength and the additional labor costs to mold plastic bearings with retractable cores result in plastic bearings that are relatively expensive to manufacture in the United States. However, an open-and-shut molding process to manufacture plastic bearings and an assembly process which does not require force on bearings could greatly reduce manufacturing costs.
The present invention solves the problem of making small-diameter plastic bearings domestically. Manufacturing the bearings of the invention is inexpensive. The invention uses bearings frictionally mounted in paint rollers that can have an internal diameter smaller than the conventional one- and one-half-inch diameter. An open-and-shut molding process results in one-piece bearing with a central opening. In addition, an offsetting relationship of the frictional support surfaces on the bearing diminishes the criticality of dimensional tolerances, thus allowing the inexpensive manufacture of small-diameter bearings that properly engage the interior of a paint roller core in a hand slip-on or manual arrangement. Open-and-shut molding considerably reduces labor costs of manufacturing one-piece bearings and an assembly process using a separate axle-engaging member greatly reduces the forces on the bearing during assembly on the paint roller frame. Consequently, manufacture of the bearings from inexpensive grades of plastics is feasible.
A preferred embodiment of this bearing housing creates the continuous axle core through an offsetting relationship of frictional support surfaces that require a simple open-and-shut mold design, one which does not require cores or slides. Another preferred embodiment uses oppositely positioned friction ridges to provide regions of higher frictional engagement between the bearing and the roller.